#!/usr/bin/perl
use strict;
use warnings;

use Storable;

my %h2;
my %hash = (

    'roster' => {
        'mike' => 'biology',
        'carol' => 'math',
        'tom'   => 'history',
    },

    'courses' => {
        'math' => 'full',
        'biology' => 'open',
        'art' => 'open',
    }
);

store(\%hash, "test.dat");
%h2 = %{retrieve "test.dat"};

for (sort keys %h2) {
    print $_, " ", %{$h2{$_}};
}